1. Field of the Invention
The present invention relates to a blade assembly for a hydraulic power transmitting apparatus and a method of manufacturing the blade assembly. The blade assembly is for use in a pump or a turbine of a hydraulic power transmitting apparatus and is made of a metallic plate by fixing blades to a shell.
2. Description of Related Art
An art of manufacturing a blade assembly of a hydraulic power transmitting apparatus by pressing it from a metallic plate is disclosed, e.g., in Japanese Published Unexamined Patent Application Nos. 4496/1995, 42413/1997, or the like.
In the art disclosed in Japanese Published Unexamined Patent Application No. 4496/1995, a semi-manufactured product having a plurality of blades disposed between a ring on an outer periphery and a ring on an inner periphery is formed from a single metallic plate by pressing or punching. The blades are twisted to thereby form a blade assembly. Two blade assemblies are combined into one while the blade position is shifted by an amount corresponding to one pitch or half the pitch, and are welded together to the shell. According to this art, a square metallic plate one side of which corresponds to the diameter of the blade assembly is required. This square plate will result in substantially triangular waste plate pieces (i.e., scraps) at each four corner of the metallic plate, and in a circular scrap plate in the center thereof, resulting in much waste of the material. In addition, by combining two blade assemblies into one, the weight increases because there are two rings on an outer periphery and on an inner periphery, respectively.
On the other hand, in the art disclosed in Japanese Published Unexamined Patent Application No. 42413/1997, a band-shaped metallic plate is used as a raw material. There are punched out a metallic plate having two parallelly disposed tie members and blade portion which is connected to both the above-described tie members. One of the tie members is slightly bent into a ring shape to thereby form an outer peripheral pitch. The other of the tie members is bent, by an amount larger than that of the above-described one of the tie members, into a ring shape to thereby form an inner peripheral pitch. According to this means, much time is required in bending the tie members, and the weight of the blade assembly increases due to the presence of the bent portions.
In view of the above-described points in the prior art, the present invention has an object of providing a blade assembly and a method of manufacturing the same in which the blade assembly can be manufactured easily with a minimum waste in the raw material and in which the blade assembly can be fixed to the shell without adversely affecting the power transmitting efficiency.
In order to attain the above and other objects, the present invention is a blade assembly for a hydraulic power transmitting apparatus. The blade assembly comprises: a plurality of blades disposed at an equal distance from one another; a joint piece provided at a radially outer end of each of the blades; and a tie member for tying the blades together at the joint pieces, wherein the blades, the joint pieces and the tie member are integrally formed as a continuous semi-manufactured product of a belt-shaped metal plate, each of the blades being erected from a plane including said tie member, the joint pieces being bent to change a direction of the tie member, and the tie member containing therein a required number of blades being fixedly joined together at both ends thereof into a ring shape.
According to this arrangement, since the blade assembly is made up of the blades and the tie member which constitute a continuous product, there is no extra or overlapped portion. Therefore, the blade assembly can be made light in weight.
Preferably, the tie member of the blade assembly is fixedly connected to a shell outside an imaginary line which connects an outer peripheral line of fluid flow between a pump and a turbine. According to this arrangement, the portion connecting the blade assembly to the shell does not hinder the flow of the working fluid in the blade assembly. Therefore, the efficiency of power transmission does not become poor.
Preferably, the blade assembly is disposed on a pump side and the tie member of the blade assembly encloses an outer periphery of the turbine at a small clearance. According to this arrangement, since the tie member encloses the outer periphery of the turbine at a small clearance, the flow of the working fluid toward the outer periphery can be minimized and is caused to flow smoothly toward the turbine side. As a result, the efficiency of power transmission can be improved.
Preferably, in the blade assembly, an outer periphery of the tie member and an outer edge of each of the blades are brazed to the shell. According to this arrangement, the area of brazing is large with a large mechanical strength. Especially in the outer periphery of the pump in which a large centrifugal force operates, since the blades are brazed at their outer edge, the mechanical strength is high. Most preferably, to secure a still higher mechanical strength, the joint piece shall also be brazed.
In another aspect of the present invention, there is provided a method of manufacturing a blade assembly for a hydraulic power transmitting apparatus. The method comprises the steps of: feeding a belt-shaped metal plate in a longitudinal direction thereof; punching the metal plate to obtain a continuous semi-manufactured product having therein a plurality of blades and a pair of tie members to which a radially outer end and a radially inner end of each of the blades are connected, respectively; removing that one of the tie members which is connected to the inner end of each of the blades; twisting each of the blades to thereby raise each of the blades from a plane which includes the other of the tie members; bending each of joint pieces which are connected to the other of the tie members to thereby change a direction of the joint pieces; cutting the other of the tie members to thereby obtain a semi-manufactured product which contains therein a required number of blades; and fixedly joining the other of the tie members at both ends thereof into a ring shape.
According to this method, the tie member is bent at the joint pieces into a ring shape. Therefore, the bending into the ring shape can be made easily, resulting in an easy forming of the ring-shaped blade assembly.